Our Milky Way: Lost And Lonely In The Void

Wherever we look in the Universe, we see the same bizarre foam-like pattern–heavy, invisible filaments of mysterious dark matter braiding themselves around each other, weaving a gigantic structure called the Cosmic Web. The filaments are on fire with the light of dancing stars, that trace out these massive transparent filaments, casting light on that which otherwise cannot be seen with human eyes. Brilliant, star-blazing, enormous galaxies can be observed swarming like sparkling fireflies around the borders of enormous, black, and almost–but not entirely–empty Voids, which interrupt this strange, twisting, invisible web-like structure. We live in a mysterious Universe that keeps its secrets well, largely because most of it is “missing”–evading the prying eyes of those who seek to explore that which is hidden, unknown, and possibly lost to us forever beyond the horizon of our visibility. Those extremely distant objects are located in unimaginably remote regions, and their traveling light has not had enough time to reach us since the Big Bang birth of Space and Time almost 14 billion years ago–as a result of the expansion of the Universe. At the June 2017 meeting of the American Astronomical Society (AAS) in Austin, Texas, astrophysicists announced that they had uncovered one of our Universe’s secrets–our Galaxy dwells within a dark Void.

When we consider our vast Universe as a whole, our large spiral Milky Way Galaxy and its “near” neighbors are in the far suburbs. In a 2013 observational study, University of Wisconsin-Madison astronomer Dr. Amy Barger and her then-student Ryan Keenan demonstrated that our Milky Way, in the context of the large-scale structure of the Universe, is situated within an almost-empty Void. Here, in this relatively lonely place in Space, there are far fewer galaxies, stars, and planets than expected. Keenan is currently at Udacity in Mountain View, California.

This new study, conducted by a University of Wisconsin-Madison undergraduate, who is also a student of Dr. Barger’s, strengthens the earlier work that proposes we are located in one of the dark and almost–but not completely–empty Voids of the great Cosmic Web. The new research also helps to reconcile some of the apparent disagreement between differing measurements of the Hubble Constant. The Hubble Constant is the unit cosmologists use to describe the current expansion rate of the Universe.

“No matter what technique you use, you should get the same value for the expansion rate of the Universe today. Fortunately, living in a Void helps resolve these tensions,” explained Ben Hoscheit on June 6, 2017 at the AAS meeting. Mr. Hoscheit is the University of Wisconsin student who found that our Milky Way Galaxy is a denizen of a much larger than average Void.

The new research is part of a more general effort to better understand the large-scale structure of the Universe. The enormous, massive, web-like structure has been likened to Swiss cheese–or, alternatively, to a natural sponge, or even a familiar honeycomb. It also resembles the neural network of the human brain. The massive filaments of the Cosmic Web are outlined by shining superclusters of galaxies and clusters of galaxies, which are in turn composed of brilliant fiery stars, glowing gas, dust, planets, moons, and other smaller objects. The two “missing” components of the Cosmos–dark matter and dark energy–cannot yet be directly observed.

The Universe is currently thought to be composed of approximately 4.9 percent “ordinary” atomic(baryonic) matter, 26.8 percent dark matter, and 84.5 percent dark energy. The two “missing” components of the total mass of the Universe, dark matter and dark energy, together constitute about 95.1 percent of the Universe’s total mass. Clearly, so-called “ordinary” atomic matter is the pathetic runt of the Universe’s litter of three. However, atomic matter is not really “ordinary” at all–this extraordinary form of matter constitutes the world that human beings are familiar with, and encompasses all of the atomic elements listed in the familiar Periodic Table. The only atomic elements manufactured in the Big Bang fireball are hydrogen, helium, and traces of lithium and beryllium. All of the heavier atomic elements were produced by way of the process of nuclear fusion by the stars or–in the case of the heaviest atomic elements–in the supernova conflagrations that marked the grand finale of their stellar existence. Dark matter is mysterious stuff, thought to be composed of exotic non-atomic particles that do not interact with light or any other form of electromagnetic radiation. However, dark matter does interact with “ordinary” atomic matter through the force of gravity, which is the reason why it gives itself away–even though it is invisible. The gravitational effects of the dark matter on visible atomic matter reveal its ghostly presence. Dark energy is even more mysterious than the dark matter. Possibly, a property of space itself, it is the substance that is causing the Universe to speed up in its expansion.

However, there is an alternative proposal to the existence of dark energy.This proposal suggests that our planet is located close to the center of a large Void. While the results seem to indicate that the Void models fit poorly with observation, nevertheless many scientists think that more research is necessary in order to determine if Void models, dark energy, or something else entirely can accurately explain how and why the Universe is expanding at an accelerating rate.

Lost In The Void

The enormous Cosmic Web accounts for more than 50 percent of the volume of the entire Universe, and its strange structure displays enormous, massive dark matter filaments surrounding vast, black, and almost empty Voids. Our Cosmos is filled with enormous collections of galaxies that are arranged into clusters and nodes that are linked together by long strings within the dark matter tendrils of the Cosmic Web. This huge structure is remarkably well-organized, and it shows some very busy intersections of galaxies buzzing around black, empty-looking spaces. The enormous, cavernous Voids have, for many years, been the target of astronomers in their efforts to understand the relatively small population of galactic constituents that swarm around them. It is difficult to tell whether the regions of shining matter and dark filaments, on fire with the sparkling flames of trillions of stars, encircle the black and almost-empty cavernous Voids, or if the Voids instead surround these massive starlit filamentary tendrils of the mysterious, ghostly, twisting and transparent stuff. Indeed, the two components of the Cosmic Web are so tangled up together that some cosmologists propose that the entire large-scale structure of the Universe can best be described as only one vast filament, lit up by fiery stars and glowing gas, and only one vast Void, knotted up together in a twisted and unimaginably enormous web.

The most recent studies show that our Universe evolved as it grew both older and colder. It was born 13.8 billion years ago, in the ripping apart of Space itself, in the exponential expansion of the inflation of the Big Bang. It started out as an unimaginably small Patch, and then–in the briefest fraction of a second–expanded exponentially to reach macroscopic size. The large-scale structure of the Universe, as observed in the Cosmic Web, may have been born with no real physical differences existing between areas of higher-than-average density, where luminous galactic structures formed within dark matter halos, and areas of lower-than-average density, which evolved into the almost-empty Voids. If the large scale structure of the Universe, as we see it today, is really the outcome of random fluctuations on the quantum level in the baby Universe, this observation is what the most straightforward cosmological models propose. In physics, a quantum is the minimum amount of any physical entity involved in interactions.

As a result, some domains of the Universe received a much greater density of matter than others, simply because of chance. As the saying goes, “the rich get richer and the poor get poorer.” Because of haphazard quantum fluctuations in the newborn Cosmos, the distribution of wealth in our Universe was completely random.

Our Milky Way: Lost And Lonely In The Void

The Void that contains our Galaxy, dubbed the KBC Void for Keenan, Barger, and the University of Hawaii’s Dr. Lennox Cowie, is thought to be at least seven times as large as the average Void, with a vast radius measuring approximately 1 billion light-years. The KBC Void is currently the largest Void known to astronomers. Ben Hoscheit’s new study, according to Dr. Barger, reveals that Ryan Keenan’s first estimations of the KBC Void–which proposes that it is spherical in shape, sporting a shell of increasing thickness that is composed of galaxies, stars, and other forms of matter—is not ruled out by other observational constraints.

“It is often really hard to find consistent solutions between many different observations. What Ben has shown is that the density profile that Keenan measured is consistent with cosmological observables. One always wants to find consistency, or else there is a problem somewhere that needs to be resolved,” Dr. Barger noted at the June 2017 AAS meeting. Dr. Barger is an observational cosmologist who holds an affiliate graduate appointment at the University of Hawaii’s Department of Physics and Astronomy.

For scientists, who are measuring the accelerated expansion of the Universe, the brilliant light that goes shrieking out into space from a Type Ia supernova is the standard candle of choice. Type Iasupernovae all explode with the same amount of energy, and because of this they can provide astronomers with a method to measure the Hubble Constant. The discovery of the dark energy itself, back in 1998, was made by astronomers using Type Ia supernovae as standard candles.

As an alternative method, the cosmic microwave background (CMB) is also a way for astronomers to probe the primordial Universe. The CMB is the relic light of the Big Bang itself.

“Photons from the CMB encode a baby picture of the very early Universe. They show us that at that stage, the Universe was surprisingly homogeneous. It was a hot, dense soup of photons, electrons and protons, showing only minute temperature differences across the sky. But, in fact, those tiny temperature differences are exactly what allow us to infer the Hubble Constant and the ‘local’ determination derived from observations of light from relatively nearby supernovae,” Ben Hoscheit explained at the June 2017 meeting of the AAS.

Hoscheit continued to explain that a direct comparison can therefore be made between the “cosmic” determination of the Hubble Constant and the “local” determination derived from observations of light from relatively nearby supernovae.

Dr. Barger noted that this new study, conducted by Hoscheit, shows that there are no current observational obstacles to the conclusion that the Milky Way resides in a very large Void. She added that, as a bonus, the presence of the Void can also resolve some of the discrepancies between techniques used to clock how fast the Universe is expanding.

Judith E. Braffman-Miller is a writer and astronomer whose articles have been published since 1981 in various magazines, newspapers, and journals. Although she has written on a variety of topics, she particularly loves writing about astronomy because it gives her the opportunity to communicate to others the many wonders of her field. Her first book, “Wisps, Ashes, and Smoke,” will be published soon.